HHR vs. Cobalt - Parts
 

Will the downpipe for a Cobalt T/C fit on my HHR SS T/C? Since both cars use the same platform, is the complete exhaust system interchangeable between the cars? Do they both use the same motor/transmission mounts?

You might want to give Josh a shout at OTTPerformance. I bought their sway bar and Pedders springs, both listed on their site for a cobalt SS. Talking to Josh, he said lots of parts are interchangable. He could give you the straight anwers you're looking for. "Moon"

The down pipe fits for sure, I had a ZZP catless down pipe I took off and sold last week and just installed the ZZP spun cat down pipe yesterday. Both were for an 08+ cobalt SS/TC.
I wouldn't bother with the rest of the exhaust unless you just want one. It would be cheaper to have a muffler and/or resonator swapped out for the sound you want. There are dyno results on CobaltSS.net, where all the guy did was swap out a stock exhaust for a 3" aftermarket and he only gained 5whp & 7wtq on his Cobalt SS/TC (besides a different sound). A bigger exhaust isn't going to make huge gains unless you go to a big turbo, you can't argue with the dyno results. SO unless you just want an easier bolt on installation, for sound, having a new muffler and/or resonator welded on/off (depending what sound your going for) would be better.

I believe that the 2 rear exhaust hangars are slightly different.

Downpipe
 

Thanks HHRSSouth for the info. I'm gonna order a catless MPx pipe tonight. Will the catless downpipe make much sound difference? My car has 12k miles. As far as the rest of the exhaust, I'm not planning on replacing anything soon. I do have a Spintec muffler on my Fiero that I may weld on. I also have a Mac muffler (a lot like a Flowmaster 40) that was part of a catback system on my '96 5.0 Explorer. I'll wait to see what sound changes occur w/the downpipe.

i say get get rid of all restrictions. with a catless 3in dp all the way back,you can pick up a good 15hp,untuned.

Yes a catless dp will make a difference in sound on the stock exhaust. I would start there and decide if its loud enough for you. I actually think the Catless down pipe with muffler delete and keeping the resonator sounds better the leaving both the resonator and muffler on with a catless down pipe. There are sound clips on youtube of the Cobalt SS/TC of both. Make sure whatever muffler (if you keep one) you put on its a straight through design, not chambered so you get max flow. Dynomax has a new VT series muffler that just came out (drone free muffler) that I actually bought to put on my turbo van project.

Be prepared, a catless downpipe on cold start up sounds like a angry lawn mower till its gets out of the warm up mode, then it sounds pretty sweet.

Be careful, I see you have an automatic tranny. They are positioned about an inch farther forward and change the length of the exhaust system compared to a 5spd HHR. Not sure how that compares with a cobalt, but I would check it first.

^^^^ Good point I would definetly make sure you call them first for an automatic :thumb:

its possible to pick up 15hp tuned, but its not going to happen untuned. not only will the engine end up adjusting the airload down after time, but even even with a custom tune your only going to pick up about 15hp with a full 3" catless turboback exhaust. plus the catback will set you back abour 3x the cost of the downpipe itself and will only increase roughly 5hp at max. 5hp for $400+ doesn't seem worth it to me. the downpipe swap will make the turbo spool up sooner even on the stock tune, friend of mine made about 250/250 on his cobalt with airbox mod, k&n drop in, and a full 3" catless turboback on the stock tune. he gained less than 10hp and tq with those mods.